Re: Custom ICC Profiles/Conversion Rending Intents
Re: Custom ICC Profiles/Conversion Rending Intents
- Subject: Re: Custom ICC Profiles/Conversion Rending Intents
- From: Graeme Gill <email@hidden>
- Date: Mon, 20 Jun 2005 21:51:42 +1000
- Organization: Argyll CMS
Chris Murphy wrote:
This is a valid question and raises all kinds of additional questions
as well. However I was speaking more from a generic sense. Clearly 400%
heavy GCR with the vast majority of devices out there, is a
contradiction of sorts. You really don't have such a high ink limit and
a high black generation.
You seem to be treating the ink limit as goal rather than a limit.
As a limit, does it matter if (with a certain GCR) it is never approached ?
It can't make any difference to the color.
GCR is a secondary preference, that shouldn't affect the gamut size
or color reproduction.
Ahh but it very clearly does with the way it's generally implemented
today, as a relative setting, rather than an absolute setting
explicitly tied to ink limit. High GCR does clearly improve shadow
gamut quite a bit (while potentially obliterating shadow detail,
depending on the output device's propensity to plug in shadows).
Maybe it does on some packages, but by my view, they are doing
it incorrectly.
The silly part, and ultimately my complaint, has nothing to do with
math. It has to do with the whole concept of an ink limit. What we have
here is a legal loophole. Legal mathematically, but not a good idea in
practice.
It's not a "loophole", its just a practical implementation peculiarity of
of Lut profiles.
By 17%. Depending on the printing process, this could be a big problem.
Most likely it's an annoyance, or "not ideal" but that 17% could
actually cause problems in drying, off set, unnecessary ink
consumption, etc. I don't like the idea that an "ink limit" is
considered a suggestion, even if it can be explained mathematically.
It is something that can be compensated for, either by software, or
by the profiler. Usually it is the latter. If the method of setting
an ink limit is to try a few ink limits, and look at the results,
then it doesn't much matter if you get a good result by setting
a 260% ink limit, and the actual ink limit is 273%. It's just a number,
and things work if it is set to the right value.
Yes. I'd like to see a black generation tag. It means some work on the
part of the ICC to separate the ambiguous from unambiguous varieties of
black generation (I think completely unambiguity isn't going to
happen), but it would be very useful metadata to have for repurposing
separations.
But there is/was a black generation tag - icSigUcrBgTag. It consists of two curves,
one for UCR, and one for black generation. Good luck on figuring out what the curve
actually means however, because the ICC spec. doesn't say. It's also been dropped
from the V4.1 spec. and beyond I notice.
Graeme Gill.
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